The narwhal is the unicorn of the sea, a pale-colored porpoise found in Arctic coastal waters and rivers. These legendary animals have two teeth. In males, the more prominent tooth grows into a swordlike, spiral tusk up to 8.8 feet (2.7 meters) long. The ivory tusk tooth grows right through the narwhal's upper lip. Scientists are not certain of the tusk's purpose, but some believe it is prominent in mating rituals, perhaps used to impress females or to battle rival suitors. Females sometimes grow a small tusk of their own, but it does not become as prominent as the male's.

Narwhals grow very slowly in the cold Arctic waters, attain lengths from 13 to 20 feet (4 to 6.1 meters), and can weigh 3,500 pounds (1,600 kilograms). They have black marbled back with lighter bellies. They are darkest when born and become whiter in color with age.

Like other porpoises, they will travel in groups and they feed on fish, shrimp, squid, and other aquatic fare. Their hunting groups are around 15 to 20 narwhals. They are also known not only for their tusk but their ability to perform deep dives. When on their wintering grounds, the narwhals make some of the deepest dives ever recorded for a marine mammal. These dives go at least 800 meters (2,400 feet) over 15 times per day with many dives reaching 1,500 meters (4,500 feet). To make this dive to these depths it last around 25 minutes, including the time spent at the bottom.The predators of the narwhal are polar bears, human hunters, and walruses.

The narwhal is common in northern parts of Greenland, mostly out at sea, though sometimes in fjords. The narwhale, like the beluga, makes seasonal group migrations. In April they travel northwards towards Qaanaaq, and can be seen in summer at Inglefield Bredning amongst other places. Also they migrate southwards in Oct-Nov and winters in Baffin Bay. The narwhal is only spotted occasionally south of Kangerlussuaq. They can be seen in East Greenland as far north as Danmarkshavn and on, rare occasions, right up to Independence Fjord.

Inuit people hunt the narwhal for their long tusks and their skin, or muktuk, an important source of vitamin C in the traditional Arctic diet. The muktuk is also used for raw skin and blubber, these are considered a delicacy, and the bones are used for tools and art. The narwhal's legend of its tusk was that it was created when a woman with a harpoon rope tied around her waist got pulled through the ocean by a large narwhal. As she was getting dragged she was transformed into a narwhal and her hair, being a twisted knot, became the spiral narwhal tusk.

The European legend is that the narwhal tusks used to be the horns from the legendary unicorn. The tusks of the narwhal were considered to have magic powers, such as healing poison and melancholia.